INVESTIGATIONS SINCE MENDEL 551 
due to the absence of the factor for tallness. Since the presence 
and absence hypothesis explains more cases than the dominant 
and recessive hypothesis, it has been generally accepted. 
Again Mendel worked chiefly with qualitative characters, which 
have been found to behave differently from most quantitative 
characters, such as size and weight. For example, in crossing large 
and small varieties of Corn, the individuals of the first hybrid gen- 
remaieeetite 
thadensvccecegces 
GREP ERE TERT TERED ¢ . <<. 
alBeogugecenqeetene cone 
Tes 
Fic. 480. — Inheritance of length of ears in Corn. The ears P; are ears 
of the parent plants (Tom Thumb Pop Corn at the left and Purple Flint Corn 
at the right) chosen to represent the average length of ears of parents. Notice 
that the ear of the F; generation is intermediate in length between the paren- 
tal ears, while in the F. generation, as shown by the ears at the left and right 
of the F; ear, the length of ears range from that of Tom Thumb Pop to that 
of Purple Flint. After East. 
eration are intermediate in size between the parents, the size of 
neither parent dominating, and in the second hybrid generation 
the individuals are of various sizes, ranging from that of the 
smaller to that of the larger parent (Figs. 479, 480 and 481). 
At first such cases were considered striking exceptions to Men- 
del’s law. However, a more careful study has led to the view 
that quantitative characters do mendelize but commoniy depend 
upon so many independent factors, each of which is responsible 
